Blue-Eyed Humans May All Descend from a Single, Common Ancestor

Do you have blue eyes? You may have more in common than other blue-eyed individuals than you once thought. Scientists have found that people with blue eyes have a single, common ancestor.

"Originally, we all had brown eyes," said Hans Eiberg, one of the researchers, in a news release. "But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes."

The OCA2 gene codes for the so-called P protein. This protein is involved in the production of melanin, which is the pigment that gives color to our hair, eyes and skin. The "switch," which is located in the gene adjacent to OCA2 does not turn off the gene entirely. Instead, it limits its action to reducing the production of melanin in the iris, effectively "diluting" brown eyes to blue. If OCA2 is completely destroyed or turned off, it leads to a condition known as albinism.

Variation in the color of the eyes from brown to green can all be explained by the amount of melanin in the iris. However, blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. Because of this, researchers can conclude that all blue-eyed individuals are linked to the same ancestor.

In this latest study, the researchers examined mitochondrial DNA and compared the eye color of blue-eyed individuals in countries as diverse as Jordan, Denmark and Turkey. This revealed that the OCA2 gene is responsible for eye color.

"They have all inherited the same switch at exactly the same spot in their DNA," said Eiberg.

In contrast, brown eyed individuals have considerable individual variation in the area of their DNA that controls melanin production.

The findings reveal a bit more about the appearance of blue eyes. It also shows researchers a bit more about the genetics of humans in general.